It is well known that moisture, as well as other liquids and gases, e.g., hydrogen sulfide and sulfur dioxide, attack metallic surfaces and cause corrosion in the form of pitting and rust formation. A common method for preventing such corrosion is the application of a coating composition which is impervious to such corrosive fluids over the metal surface. The coating composition acts as a barrier which prevents contact between the metal surface and its corrosive environment.
One type of coating composition known to be useful in protecting metal surfaces is a wax-like coating composition having a lanolin base. Lanolin-based coating compositions exhibit strong adherence to the metal surface, and cracks in the coating do not easily occur.
Lanolin is generally available in either a hydrous form, containing about 25% to 30% water, or in an anhydrous form, typically containing no more than about 0.25% water. It is the anhydrous form of lanolin which is generally used in corrosion inhibiting coating compositions. This is because lanolin tends to be a good solubilizer of oxygen and, if water is present in such compositions, it may be surrounded by oxygen at a concentration greater than that in the water. Under such conditions, if the water is in contact with the metal surface, corrosion is likely to occur.
Lanolin is the refined product of wool grease, the "fat-like" secretion of the sebaceous glands of sheep which is deposited onto the sheep's wool fibers. Lanolin is made up of a complex mixture of esters and polyesters of high molecular weight alcohols and fatty acids.
Unrefined wool grease contains, in addition to the complex mixture of esters and polyesters present in lanolin, free alcohols and fatty acids and water in an amount typically less than about 10% by weight. Because of its relatively high moisture content and the presence of free fatty acids, unrefined wool grease is generally not used in corrosion inhibiting coating compositions.